xref: /freebsd/sys/netinet/tcp_output.c (revision 3e8eb5c7f4909209c042403ddee340b2ee7003a5)
1 /*-
2  * SPDX-License-Identifier: BSD-3-Clause
3  *
4  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995
5  *	The Regents of the University of California.  All rights reserved.
6  *
7  * Redistribution and use in source and binary forms, with or without
8  * modification, are permitted provided that the following conditions
9  * are met:
10  * 1. Redistributions of source code must retain the above copyright
11  *    notice, this list of conditions and the following disclaimer.
12  * 2. Redistributions in binary form must reproduce the above copyright
13  *    notice, this list of conditions and the following disclaimer in the
14  *    documentation and/or other materials provided with the distribution.
15  * 3. Neither the name of the University nor the names of its contributors
16  *    may be used to endorse or promote products derived from this software
17  *    without specific prior written permission.
18  *
19  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
21  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
22  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
23  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
24  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
25  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
26  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
27  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
28  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
29  * SUCH DAMAGE.
30  *
31  *	@(#)tcp_output.c	8.4 (Berkeley) 5/24/95
32  */
33 
34 #include <sys/cdefs.h>
35 __FBSDID("$FreeBSD$");
36 
37 #include "opt_inet.h"
38 #include "opt_inet6.h"
39 #include "opt_ipsec.h"
40 #include "opt_kern_tls.h"
41 #include "opt_tcpdebug.h"
42 
43 #include <sys/param.h>
44 #include <sys/systm.h>
45 #include <sys/arb.h>
46 #include <sys/domain.h>
47 #ifdef TCP_HHOOK
48 #include <sys/hhook.h>
49 #endif
50 #include <sys/kernel.h>
51 #ifdef KERN_TLS
52 #include <sys/ktls.h>
53 #endif
54 #include <sys/lock.h>
55 #include <sys/mbuf.h>
56 #include <sys/mutex.h>
57 #include <sys/protosw.h>
58 #include <sys/qmath.h>
59 #include <sys/sdt.h>
60 #include <sys/socket.h>
61 #include <sys/socketvar.h>
62 #include <sys/sysctl.h>
63 #include <sys/stats.h>
64 
65 #include <net/if.h>
66 #include <net/route.h>
67 #include <net/route/nhop.h>
68 #include <net/vnet.h>
69 
70 #include <netinet/in.h>
71 #include <netinet/in_kdtrace.h>
72 #include <netinet/in_systm.h>
73 #include <netinet/ip.h>
74 #include <netinet/in_pcb.h>
75 #include <netinet/ip_var.h>
76 #include <netinet/ip_options.h>
77 #ifdef INET6
78 #include <netinet6/in6_pcb.h>
79 #include <netinet/ip6.h>
80 #include <netinet6/ip6_var.h>
81 #endif
82 #include <netinet/tcp.h>
83 #define	TCPOUTFLAGS
84 #include <netinet/tcp_fsm.h>
85 #include <netinet/tcp_log_buf.h>
86 #include <netinet/tcp_seq.h>
87 #include <netinet/tcp_var.h>
88 #include <netinet/tcp_syncache.h>
89 #include <netinet/tcp_timer.h>
90 #include <netinet/tcpip.h>
91 #include <netinet/cc/cc.h>
92 #include <netinet/tcp_fastopen.h>
93 #ifdef TCPPCAP
94 #include <netinet/tcp_pcap.h>
95 #endif
96 #ifdef TCPDEBUG
97 #include <netinet/tcp_debug.h>
98 #endif
99 #ifdef TCP_OFFLOAD
100 #include <netinet/tcp_offload.h>
101 #endif
102 #include <netinet/tcp_ecn.h>
103 
104 #include <netipsec/ipsec_support.h>
105 
106 #include <netinet/udp.h>
107 #include <netinet/udp_var.h>
108 #include <machine/in_cksum.h>
109 
110 #include <security/mac/mac_framework.h>
111 
112 VNET_DEFINE(int, path_mtu_discovery) = 1;
113 SYSCTL_INT(_net_inet_tcp, OID_AUTO, path_mtu_discovery, CTLFLAG_VNET | CTLFLAG_RW,
114 	&VNET_NAME(path_mtu_discovery), 1,
115 	"Enable Path MTU Discovery");
116 
117 VNET_DEFINE(int, tcp_do_tso) = 1;
118 SYSCTL_INT(_net_inet_tcp, OID_AUTO, tso, CTLFLAG_VNET | CTLFLAG_RW,
119 	&VNET_NAME(tcp_do_tso), 0,
120 	"Enable TCP Segmentation Offload");
121 
122 VNET_DEFINE(int, tcp_sendspace) = 1024*32;
123 #define	V_tcp_sendspace	VNET(tcp_sendspace)
124 SYSCTL_INT(_net_inet_tcp, TCPCTL_SENDSPACE, sendspace, CTLFLAG_VNET | CTLFLAG_RW,
125 	&VNET_NAME(tcp_sendspace), 0, "Initial send socket buffer size");
126 
127 VNET_DEFINE(int, tcp_do_autosndbuf) = 1;
128 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto, CTLFLAG_VNET | CTLFLAG_RW,
129 	&VNET_NAME(tcp_do_autosndbuf), 0,
130 	"Enable automatic send buffer sizing");
131 
132 VNET_DEFINE(int, tcp_autosndbuf_inc) = 8*1024;
133 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_inc, CTLFLAG_VNET | CTLFLAG_RW,
134 	&VNET_NAME(tcp_autosndbuf_inc), 0,
135 	"Incrementor step size of automatic send buffer");
136 
137 VNET_DEFINE(int, tcp_autosndbuf_max) = 2*1024*1024;
138 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_max, CTLFLAG_VNET | CTLFLAG_RW,
139 	&VNET_NAME(tcp_autosndbuf_max), 0,
140 	"Max size of automatic send buffer");
141 
142 VNET_DEFINE(int, tcp_sendbuf_auto_lowat) = 0;
143 #define	V_tcp_sendbuf_auto_lowat	VNET(tcp_sendbuf_auto_lowat)
144 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto_lowat, CTLFLAG_VNET | CTLFLAG_RW,
145 	&VNET_NAME(tcp_sendbuf_auto_lowat), 0,
146 	"Modify threshold for auto send buffer growth to account for SO_SNDLOWAT");
147 
148 /*
149  * Make sure that either retransmit or persist timer is set for SYN, FIN and
150  * non-ACK.
151  */
152 #define TCP_XMIT_TIMER_ASSERT(tp, len, th_flags)			\
153 	KASSERT(((len) == 0 && ((th_flags) & (TH_SYN | TH_FIN)) == 0) ||\
154 	    tcp_timer_active((tp), TT_REXMT) ||				\
155 	    tcp_timer_active((tp), TT_PERSIST),				\
156 	    ("neither rexmt nor persist timer is set"))
157 
158 static void inline	cc_after_idle(struct tcpcb *tp);
159 
160 #ifdef TCP_HHOOK
161 /*
162  * Wrapper for the TCP established output helper hook.
163  */
164 void
165 hhook_run_tcp_est_out(struct tcpcb *tp, struct tcphdr *th,
166     struct tcpopt *to, uint32_t len, int tso)
167 {
168 	struct tcp_hhook_data hhook_data;
169 
170 	if (V_tcp_hhh[HHOOK_TCP_EST_OUT]->hhh_nhooks > 0) {
171 		hhook_data.tp = tp;
172 		hhook_data.th = th;
173 		hhook_data.to = to;
174 		hhook_data.len = len;
175 		hhook_data.tso = tso;
176 
177 		hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_OUT], &hhook_data,
178 		    tp->osd);
179 	}
180 }
181 #endif
182 
183 /*
184  * CC wrapper hook functions
185  */
186 static void inline
187 cc_after_idle(struct tcpcb *tp)
188 {
189 	INP_WLOCK_ASSERT(tp->t_inpcb);
190 
191 	if (CC_ALGO(tp)->after_idle != NULL)
192 		CC_ALGO(tp)->after_idle(tp->ccv);
193 }
194 
195 /*
196  * Tcp output routine: figure out what should be sent and send it.
197  */
198 int
199 tcp_default_output(struct tcpcb *tp)
200 {
201 	struct socket *so = tp->t_inpcb->inp_socket;
202 	int32_t len;
203 	uint32_t recwin, sendwin;
204 	uint16_t flags;
205 	int off, error = 0;	/* Keep compiler happy */
206 	u_int if_hw_tsomaxsegcount = 0;
207 	u_int if_hw_tsomaxsegsize = 0;
208 	struct mbuf *m;
209 	struct ip *ip = NULL;
210 #ifdef TCPDEBUG
211 	struct ipovly *ipov = NULL;
212 #endif
213 	struct tcphdr *th;
214 	u_char opt[TCP_MAXOLEN];
215 	unsigned ipoptlen, optlen, hdrlen, ulen;
216 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
217 	unsigned ipsec_optlen = 0;
218 #endif
219 	int idle, sendalot, curticks;
220 	int sack_rxmit, sack_bytes_rxmt;
221 	struct sackhole *p;
222 	int tso, mtu;
223 	struct tcpopt to;
224 	struct udphdr *udp = NULL;
225 	unsigned int wanted_cookie = 0;
226 	unsigned int dont_sendalot = 0;
227 #if 0
228 	int maxburst = TCP_MAXBURST;
229 #endif
230 #ifdef INET6
231 	struct ip6_hdr *ip6 = NULL;
232 	int isipv6;
233 
234 	isipv6 = (tp->t_inpcb->inp_vflag & INP_IPV6) != 0;
235 #endif
236 #ifdef KERN_TLS
237 	const bool hw_tls = (so->so_snd.sb_flags & SB_TLS_IFNET) != 0;
238 #else
239 	const bool hw_tls = false;
240 #endif
241 
242 	NET_EPOCH_ASSERT();
243 	INP_WLOCK_ASSERT(tp->t_inpcb);
244 
245 #ifdef TCP_OFFLOAD
246 	if (tp->t_flags & TF_TOE)
247 		return (tcp_offload_output(tp));
248 #endif
249 
250 	/*
251 	 * For TFO connections in SYN_SENT or SYN_RECEIVED,
252 	 * only allow the initial SYN or SYN|ACK and those sent
253 	 * by the retransmit timer.
254 	 */
255 	if (IS_FASTOPEN(tp->t_flags) &&
256 	    ((tp->t_state == TCPS_SYN_SENT) ||
257 	     (tp->t_state == TCPS_SYN_RECEIVED)) &&
258 	    SEQ_GT(tp->snd_max, tp->snd_una) && /* initial SYN or SYN|ACK sent */
259 	    (tp->snd_nxt != tp->snd_una))       /* not a retransmit */
260 		return (0);
261 
262 	/*
263 	 * Determine length of data that should be transmitted,
264 	 * and flags that will be used.
265 	 * If there is some data or critical controls (SYN, RST)
266 	 * to send, then transmit; otherwise, investigate further.
267 	 */
268 	idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una);
269 	if (idle && (((ticks - tp->t_rcvtime) >= tp->t_rxtcur) ||
270 	    (tp->t_sndtime && ((ticks - tp->t_sndtime) >= tp->t_rxtcur))))
271 		cc_after_idle(tp);
272 	tp->t_flags &= ~TF_LASTIDLE;
273 	if (idle) {
274 		if (tp->t_flags & TF_MORETOCOME) {
275 			tp->t_flags |= TF_LASTIDLE;
276 			idle = 0;
277 		}
278 	}
279 again:
280 	/*
281 	 * If we've recently taken a timeout, snd_max will be greater than
282 	 * snd_nxt.  There may be SACK information that allows us to avoid
283 	 * resending already delivered data.  Adjust snd_nxt accordingly.
284 	 */
285 	if ((tp->t_flags & TF_SACK_PERMIT) &&
286 	    SEQ_LT(tp->snd_nxt, tp->snd_max))
287 		tcp_sack_adjust(tp);
288 	sendalot = 0;
289 	tso = 0;
290 	mtu = 0;
291 	off = tp->snd_nxt - tp->snd_una;
292 	sendwin = min(tp->snd_wnd, tp->snd_cwnd);
293 
294 	flags = tcp_outflags[tp->t_state];
295 	/*
296 	 * Send any SACK-generated retransmissions.  If we're explicitly trying
297 	 * to send out new data (when sendalot is 1), bypass this function.
298 	 * If we retransmit in fast recovery mode, decrement snd_cwnd, since
299 	 * we're replacing a (future) new transmission with a retransmission
300 	 * now, and we previously incremented snd_cwnd in tcp_input().
301 	 */
302 	/*
303 	 * Still in sack recovery , reset rxmit flag to zero.
304 	 */
305 	sack_rxmit = 0;
306 	sack_bytes_rxmt = 0;
307 	len = 0;
308 	p = NULL;
309 	if ((tp->t_flags & TF_SACK_PERMIT) && IN_FASTRECOVERY(tp->t_flags) &&
310 	    (p = tcp_sack_output(tp, &sack_bytes_rxmt))) {
311 		uint32_t cwin;
312 
313 		cwin =
314 		    imax(min(tp->snd_wnd, tp->snd_cwnd) - sack_bytes_rxmt, 0);
315 		/* Do not retransmit SACK segments beyond snd_recover */
316 		if (SEQ_GT(p->end, tp->snd_recover)) {
317 			/*
318 			 * (At least) part of sack hole extends beyond
319 			 * snd_recover. Check to see if we can rexmit data
320 			 * for this hole.
321 			 */
322 			if (SEQ_GEQ(p->rxmit, tp->snd_recover)) {
323 				/*
324 				 * Can't rexmit any more data for this hole.
325 				 * That data will be rexmitted in the next
326 				 * sack recovery episode, when snd_recover
327 				 * moves past p->rxmit.
328 				 */
329 				p = NULL;
330 				goto after_sack_rexmit;
331 			} else {
332 				/* Can rexmit part of the current hole */
333 				len = ((int32_t)ulmin(cwin,
334 				    SEQ_SUB(tp->snd_recover, p->rxmit)));
335 			}
336 		} else {
337 			len = ((int32_t)ulmin(cwin,
338 			    SEQ_SUB(p->end, p->rxmit)));
339 		}
340 		off = SEQ_SUB(p->rxmit, tp->snd_una);
341 		KASSERT(off >= 0,("%s: sack block to the left of una : %d",
342 		    __func__, off));
343 		if (len > 0) {
344 			sack_rxmit = 1;
345 			sendalot = 1;
346 			TCPSTAT_INC(tcps_sack_rexmits);
347 			TCPSTAT_ADD(tcps_sack_rexmit_bytes,
348 			    min(len, tcp_maxseg(tp)));
349 		}
350 	}
351 after_sack_rexmit:
352 	/*
353 	 * Get standard flags, and add SYN or FIN if requested by 'hidden'
354 	 * state flags.
355 	 */
356 	if (tp->t_flags & TF_NEEDFIN)
357 		flags |= TH_FIN;
358 	if (tp->t_flags & TF_NEEDSYN)
359 		flags |= TH_SYN;
360 
361 	SOCKBUF_LOCK(&so->so_snd);
362 	/*
363 	 * If in persist timeout with window of 0, send 1 byte.
364 	 * Otherwise, if window is small but nonzero
365 	 * and timer expired, we will send what we can
366 	 * and go to transmit state.
367 	 */
368 	if (tp->t_flags & TF_FORCEDATA) {
369 		if (sendwin == 0) {
370 			/*
371 			 * If we still have some data to send, then
372 			 * clear the FIN bit.  Usually this would
373 			 * happen below when it realizes that we
374 			 * aren't sending all the data.  However,
375 			 * if we have exactly 1 byte of unsent data,
376 			 * then it won't clear the FIN bit below,
377 			 * and if we are in persist state, we wind
378 			 * up sending the packet without recording
379 			 * that we sent the FIN bit.
380 			 *
381 			 * We can't just blindly clear the FIN bit,
382 			 * because if we don't have any more data
383 			 * to send then the probe will be the FIN
384 			 * itself.
385 			 */
386 			if (off < sbused(&so->so_snd))
387 				flags &= ~TH_FIN;
388 			sendwin = 1;
389 		} else {
390 			tcp_timer_activate(tp, TT_PERSIST, 0);
391 			tp->t_rxtshift = 0;
392 		}
393 	}
394 
395 	/*
396 	 * If snd_nxt == snd_max and we have transmitted a FIN, the
397 	 * offset will be > 0 even if so_snd.sb_cc is 0, resulting in
398 	 * a negative length.  This can also occur when TCP opens up
399 	 * its congestion window while receiving additional duplicate
400 	 * acks after fast-retransmit because TCP will reset snd_nxt
401 	 * to snd_max after the fast-retransmit.
402 	 *
403 	 * In the normal retransmit-FIN-only case, however, snd_nxt will
404 	 * be set to snd_una, the offset will be 0, and the length may
405 	 * wind up 0.
406 	 *
407 	 * If sack_rxmit is true we are retransmitting from the scoreboard
408 	 * in which case len is already set.
409 	 */
410 	if (sack_rxmit == 0) {
411 		if (sack_bytes_rxmt == 0)
412 			len = ((int32_t)min(sbavail(&so->so_snd), sendwin) -
413 			    off);
414 		else {
415 			int32_t cwin;
416 
417                         /*
418 			 * We are inside of a SACK recovery episode and are
419 			 * sending new data, having retransmitted all the
420 			 * data possible in the scoreboard.
421 			 */
422 			len = ((int32_t)min(sbavail(&so->so_snd), tp->snd_wnd) -
423 			    off);
424 			/*
425 			 * Don't remove this (len > 0) check !
426 			 * We explicitly check for len > 0 here (although it
427 			 * isn't really necessary), to work around a gcc
428 			 * optimization issue - to force gcc to compute
429 			 * len above. Without this check, the computation
430 			 * of len is bungled by the optimizer.
431 			 */
432 			if (len > 0) {
433 				cwin = tp->snd_cwnd -
434 					(tp->snd_nxt - tp->snd_recover) -
435 					sack_bytes_rxmt;
436 				if (cwin < 0)
437 					cwin = 0;
438 				len = imin(len, cwin);
439 			}
440 		}
441 	}
442 
443 	/*
444 	 * Lop off SYN bit if it has already been sent.  However, if this
445 	 * is SYN-SENT state and if segment contains data and if we don't
446 	 * know that foreign host supports TAO, suppress sending segment.
447 	 */
448 	if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) {
449 		if (tp->t_state != TCPS_SYN_RECEIVED)
450 			flags &= ~TH_SYN;
451 		/*
452 		 * When sending additional segments following a TFO SYN|ACK,
453 		 * do not include the SYN bit.
454 		 */
455 		if (IS_FASTOPEN(tp->t_flags) &&
456 		    (tp->t_state == TCPS_SYN_RECEIVED))
457 			flags &= ~TH_SYN;
458 		off--, len++;
459 	}
460 
461 	/*
462 	 * Be careful not to send data and/or FIN on SYN segments.
463 	 * This measure is needed to prevent interoperability problems
464 	 * with not fully conformant TCP implementations.
465 	 */
466 	if ((flags & TH_SYN) && (tp->t_flags & TF_NOOPT)) {
467 		len = 0;
468 		flags &= ~TH_FIN;
469 	}
470 
471 	/*
472 	 * On TFO sockets, ensure no data is sent in the following cases:
473 	 *
474 	 *  - When retransmitting SYN|ACK on a passively-created socket
475 	 *
476 	 *  - When retransmitting SYN on an actively created socket
477 	 *
478 	 *  - When sending a zero-length cookie (cookie request) on an
479 	 *    actively created socket
480 	 *
481 	 *  - When the socket is in the CLOSED state (RST is being sent)
482 	 */
483 	if (IS_FASTOPEN(tp->t_flags) &&
484 	    (((flags & TH_SYN) && (tp->t_rxtshift > 0)) ||
485 	     ((tp->t_state == TCPS_SYN_SENT) &&
486 	      (tp->t_tfo_client_cookie_len == 0)) ||
487 	     (flags & TH_RST)))
488 		len = 0;
489 	if (len <= 0) {
490 		/*
491 		 * If FIN has been sent but not acked,
492 		 * but we haven't been called to retransmit,
493 		 * len will be < 0.  Otherwise, window shrank
494 		 * after we sent into it.  If window shrank to 0,
495 		 * cancel pending retransmit, pull snd_nxt back
496 		 * to (closed) window, and set the persist timer
497 		 * if it isn't already going.  If the window didn't
498 		 * close completely, just wait for an ACK.
499 		 *
500 		 * We also do a general check here to ensure that
501 		 * we will set the persist timer when we have data
502 		 * to send, but a 0-byte window. This makes sure
503 		 * the persist timer is set even if the packet
504 		 * hits one of the "goto send" lines below.
505 		 */
506 		len = 0;
507 		if ((sendwin == 0) && (TCPS_HAVEESTABLISHED(tp->t_state)) &&
508 			(off < (int) sbavail(&so->so_snd))) {
509 			tcp_timer_activate(tp, TT_REXMT, 0);
510 			tp->t_rxtshift = 0;
511 			tp->snd_nxt = tp->snd_una;
512 			if (!tcp_timer_active(tp, TT_PERSIST))
513 				tcp_setpersist(tp);
514 		}
515 	}
516 
517 	/* len will be >= 0 after this point. */
518 	KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
519 
520 	tcp_sndbuf_autoscale(tp, so, sendwin);
521 
522 	/*
523 	 * Decide if we can use TCP Segmentation Offloading (if supported by
524 	 * hardware).
525 	 *
526 	 * TSO may only be used if we are in a pure bulk sending state.  The
527 	 * presence of TCP-MD5, SACK retransmits, SACK advertizements and
528 	 * IP options prevent using TSO.  With TSO the TCP header is the same
529 	 * (except for the sequence number) for all generated packets.  This
530 	 * makes it impossible to transmit any options which vary per generated
531 	 * segment or packet.
532 	 *
533 	 * IPv4 handling has a clear separation of ip options and ip header
534 	 * flags while IPv6 combines both in in6p_outputopts. ip6_optlen() does
535 	 * the right thing below to provide length of just ip options and thus
536 	 * checking for ipoptlen is enough to decide if ip options are present.
537 	 */
538 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
539 	/*
540 	 * Pre-calculate here as we save another lookup into the darknesses
541 	 * of IPsec that way and can actually decide if TSO is ok.
542 	 */
543 #ifdef INET6
544 	if (isipv6 && IPSEC_ENABLED(ipv6))
545 		ipsec_optlen = IPSEC_HDRSIZE(ipv6, tp->t_inpcb);
546 #ifdef INET
547 	else
548 #endif
549 #endif /* INET6 */
550 #ifdef INET
551 	if (IPSEC_ENABLED(ipv4))
552 		ipsec_optlen = IPSEC_HDRSIZE(ipv4, tp->t_inpcb);
553 #endif /* INET */
554 #endif /* IPSEC */
555 #ifdef INET6
556 	if (isipv6)
557 		ipoptlen = ip6_optlen(tp->t_inpcb);
558 	else
559 #endif
560 	if (tp->t_inpcb->inp_options)
561 		ipoptlen = tp->t_inpcb->inp_options->m_len -
562 				offsetof(struct ipoption, ipopt_list);
563 	else
564 		ipoptlen = 0;
565 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
566 	ipoptlen += ipsec_optlen;
567 #endif
568 
569 	if ((tp->t_flags & TF_TSO) && V_tcp_do_tso && len > tp->t_maxseg &&
570 	    (tp->t_port == 0) &&
571 	    ((tp->t_flags & TF_SIGNATURE) == 0) &&
572 	    tp->rcv_numsacks == 0 && sack_rxmit == 0 &&
573 	    ipoptlen == 0 && !(flags & TH_SYN))
574 		tso = 1;
575 
576 	if (sack_rxmit) {
577 		if (SEQ_LT(p->rxmit + len, tp->snd_una + sbused(&so->so_snd)))
578 			flags &= ~TH_FIN;
579 	} else {
580 		if (SEQ_LT(tp->snd_nxt + len, tp->snd_una +
581 		    sbused(&so->so_snd)))
582 			flags &= ~TH_FIN;
583 	}
584 
585 	recwin = lmin(lmax(sbspace(&so->so_rcv), 0),
586 	    (long)TCP_MAXWIN << tp->rcv_scale);
587 
588 	/*
589 	 * Sender silly window avoidance.   We transmit under the following
590 	 * conditions when len is non-zero:
591 	 *
592 	 *	- We have a full segment (or more with TSO)
593 	 *	- This is the last buffer in a write()/send() and we are
594 	 *	  either idle or running NODELAY
595 	 *	- we've timed out (e.g. persist timer)
596 	 *	- we have more then 1/2 the maximum send window's worth of
597 	 *	  data (receiver may be limited the window size)
598 	 *	- we need to retransmit
599 	 */
600 	if (len) {
601 		if (len >= tp->t_maxseg)
602 			goto send;
603 		/*
604 		 * As the TCP header options are now
605 		 * considered when setting up the initial
606 		 * window, we would not send the last segment
607 		 * if we skip considering the option length here.
608 		 * Note: this may not work when tcp headers change
609 		 * very dynamically in the future.
610 		 */
611 		if ((((tp->t_flags & TF_SIGNATURE) ?
612 			PADTCPOLEN(TCPOLEN_SIGNATURE) : 0) +
613 		    ((tp->t_flags & TF_RCVD_TSTMP) ?
614 			PADTCPOLEN(TCPOLEN_TIMESTAMP) : 0) +
615 		    len) >= tp->t_maxseg)
616 			goto send;
617 		/*
618 		 * NOTE! on localhost connections an 'ack' from the remote
619 		 * end may occur synchronously with the output and cause
620 		 * us to flush a buffer queued with moretocome.  XXX
621 		 *
622 		 * note: the len + off check is almost certainly unnecessary.
623 		 */
624 		if (!(tp->t_flags & TF_MORETOCOME) &&	/* normal case */
625 		    (idle || (tp->t_flags & TF_NODELAY)) &&
626 		    (uint32_t)len + (uint32_t)off >= sbavail(&so->so_snd) &&
627 		    (tp->t_flags & TF_NOPUSH) == 0) {
628 			goto send;
629 		}
630 		if (tp->t_flags & TF_FORCEDATA)		/* typ. timeout case */
631 			goto send;
632 		if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
633 			goto send;
634 		if (SEQ_LT(tp->snd_nxt, tp->snd_max))	/* retransmit case */
635 			goto send;
636 		if (sack_rxmit)
637 			goto send;
638 	}
639 
640 	/*
641 	 * Sending of standalone window updates.
642 	 *
643 	 * Window updates are important when we close our window due to a
644 	 * full socket buffer and are opening it again after the application
645 	 * reads data from it.  Once the window has opened again and the
646 	 * remote end starts to send again the ACK clock takes over and
647 	 * provides the most current window information.
648 	 *
649 	 * We must avoid the silly window syndrome whereas every read
650 	 * from the receive buffer, no matter how small, causes a window
651 	 * update to be sent.  We also should avoid sending a flurry of
652 	 * window updates when the socket buffer had queued a lot of data
653 	 * and the application is doing small reads.
654 	 *
655 	 * Prevent a flurry of pointless window updates by only sending
656 	 * an update when we can increase the advertized window by more
657 	 * than 1/4th of the socket buffer capacity.  When the buffer is
658 	 * getting full or is very small be more aggressive and send an
659 	 * update whenever we can increase by two mss sized segments.
660 	 * In all other situations the ACK's to new incoming data will
661 	 * carry further window increases.
662 	 *
663 	 * Don't send an independent window update if a delayed
664 	 * ACK is pending (it will get piggy-backed on it) or the
665 	 * remote side already has done a half-close and won't send
666 	 * more data.  Skip this if the connection is in T/TCP
667 	 * half-open state.
668 	 */
669 	if (recwin > 0 && !(tp->t_flags & TF_NEEDSYN) &&
670 	    !(tp->t_flags & TF_DELACK) &&
671 	    !TCPS_HAVERCVDFIN(tp->t_state)) {
672 		/*
673 		 * "adv" is the amount we could increase the window,
674 		 * taking into account that we are limited by
675 		 * TCP_MAXWIN << tp->rcv_scale.
676 		 */
677 		int32_t adv;
678 		int oldwin;
679 
680 		adv = recwin;
681 		if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt)) {
682 			oldwin = (tp->rcv_adv - tp->rcv_nxt);
683 			if (adv > oldwin)
684 				adv -= oldwin;
685 			else
686 				adv = 0;
687 		} else
688 			oldwin = 0;
689 
690 		/*
691 		 * If the new window size ends up being the same as or less
692 		 * than the old size when it is scaled, then don't force
693 		 * a window update.
694 		 */
695 		if (oldwin >> tp->rcv_scale >= (adv + oldwin) >> tp->rcv_scale)
696 			goto dontupdate;
697 
698 		if (adv >= (int32_t)(2 * tp->t_maxseg) &&
699 		    (adv >= (int32_t)(so->so_rcv.sb_hiwat / 4) ||
700 		     recwin <= (so->so_rcv.sb_hiwat / 8) ||
701 		     so->so_rcv.sb_hiwat <= 8 * tp->t_maxseg ||
702 		     adv >= TCP_MAXWIN << tp->rcv_scale))
703 			goto send;
704 		if (2 * adv >= (int32_t)so->so_rcv.sb_hiwat)
705 			goto send;
706 	}
707 dontupdate:
708 
709 	/*
710 	 * Send if we owe the peer an ACK, RST, SYN, or urgent data.  ACKNOW
711 	 * is also a catch-all for the retransmit timer timeout case.
712 	 */
713 	if (tp->t_flags & TF_ACKNOW)
714 		goto send;
715 	if ((flags & TH_RST) ||
716 	    ((flags & TH_SYN) && (tp->t_flags & TF_NEEDSYN) == 0))
717 		goto send;
718 	if (SEQ_GT(tp->snd_up, tp->snd_una))
719 		goto send;
720 	/*
721 	 * If our state indicates that FIN should be sent
722 	 * and we have not yet done so, then we need to send.
723 	 */
724 	if (flags & TH_FIN &&
725 	    ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))
726 		goto send;
727 	/*
728 	 * In SACK, it is possible for tcp_output to fail to send a segment
729 	 * after the retransmission timer has been turned off.  Make sure
730 	 * that the retransmission timer is set.
731 	 */
732 	if ((tp->t_flags & TF_SACK_PERMIT) &&
733 	    SEQ_GT(tp->snd_max, tp->snd_una) &&
734 	    !tcp_timer_active(tp, TT_REXMT) &&
735 	    !tcp_timer_active(tp, TT_PERSIST)) {
736 		tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
737 		goto just_return;
738 	}
739 	/*
740 	 * TCP window updates are not reliable, rather a polling protocol
741 	 * using ``persist'' packets is used to insure receipt of window
742 	 * updates.  The three ``states'' for the output side are:
743 	 *	idle			not doing retransmits or persists
744 	 *	persisting		to move a small or zero window
745 	 *	(re)transmitting	and thereby not persisting
746 	 *
747 	 * tcp_timer_active(tp, TT_PERSIST)
748 	 *	is true when we are in persist state.
749 	 * (tp->t_flags & TF_FORCEDATA)
750 	 *	is set when we are called to send a persist packet.
751 	 * tcp_timer_active(tp, TT_REXMT)
752 	 *	is set when we are retransmitting
753 	 * The output side is idle when both timers are zero.
754 	 *
755 	 * If send window is too small, there is data to transmit, and no
756 	 * retransmit or persist is pending, then go to persist state.
757 	 * If nothing happens soon, send when timer expires:
758 	 * if window is nonzero, transmit what we can,
759 	 * otherwise force out a byte.
760 	 */
761 	if (sbavail(&so->so_snd) && !tcp_timer_active(tp, TT_REXMT) &&
762 	    !tcp_timer_active(tp, TT_PERSIST)) {
763 		tp->t_rxtshift = 0;
764 		tcp_setpersist(tp);
765 	}
766 
767 	/*
768 	 * No reason to send a segment, just return.
769 	 */
770 just_return:
771 	SOCKBUF_UNLOCK(&so->so_snd);
772 	return (0);
773 
774 send:
775 	SOCKBUF_LOCK_ASSERT(&so->so_snd);
776 	if (len > 0) {
777 		if (len >= tp->t_maxseg)
778 			tp->t_flags2 |= TF2_PLPMTU_MAXSEGSNT;
779 		else
780 			tp->t_flags2 &= ~TF2_PLPMTU_MAXSEGSNT;
781 	}
782 	/*
783 	 * Before ESTABLISHED, force sending of initial options
784 	 * unless TCP set not to do any options.
785 	 * NOTE: we assume that the IP/TCP header plus TCP options
786 	 * always fit in a single mbuf, leaving room for a maximum
787 	 * link header, i.e.
788 	 *	max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MCLBYTES
789 	 */
790 	optlen = 0;
791 #ifdef INET6
792 	if (isipv6)
793 		hdrlen = sizeof (struct ip6_hdr) + sizeof (struct tcphdr);
794 	else
795 #endif
796 		hdrlen = sizeof (struct tcpiphdr);
797 
798 	if (flags & TH_SYN) {
799 		tp->snd_nxt = tp->iss;
800 	}
801 
802 	/*
803 	 * Compute options for segment.
804 	 * We only have to care about SYN and established connection
805 	 * segments.  Options for SYN-ACK segments are handled in TCP
806 	 * syncache.
807 	 */
808 	to.to_flags = 0;
809 	if ((tp->t_flags & TF_NOOPT) == 0) {
810 		/* Maximum segment size. */
811 		if (flags & TH_SYN) {
812 			to.to_mss = tcp_mssopt(&tp->t_inpcb->inp_inc);
813 			if (tp->t_port)
814 				to.to_mss -= V_tcp_udp_tunneling_overhead;
815 			to.to_flags |= TOF_MSS;
816 
817 			/*
818 			 * On SYN or SYN|ACK transmits on TFO connections,
819 			 * only include the TFO option if it is not a
820 			 * retransmit, as the presence of the TFO option may
821 			 * have caused the original SYN or SYN|ACK to have
822 			 * been dropped by a middlebox.
823 			 */
824 			if (IS_FASTOPEN(tp->t_flags) &&
825 			    (tp->t_rxtshift == 0)) {
826 				if (tp->t_state == TCPS_SYN_RECEIVED) {
827 					to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
828 					to.to_tfo_cookie =
829 					    (u_int8_t *)&tp->t_tfo_cookie.server;
830 					to.to_flags |= TOF_FASTOPEN;
831 					wanted_cookie = 1;
832 				} else if (tp->t_state == TCPS_SYN_SENT) {
833 					to.to_tfo_len =
834 					    tp->t_tfo_client_cookie_len;
835 					to.to_tfo_cookie =
836 					    tp->t_tfo_cookie.client;
837 					to.to_flags |= TOF_FASTOPEN;
838 					wanted_cookie = 1;
839 					/*
840 					 * If we wind up having more data to
841 					 * send with the SYN than can fit in
842 					 * one segment, don't send any more
843 					 * until the SYN|ACK comes back from
844 					 * the other end.
845 					 */
846 					dont_sendalot = 1;
847 				}
848 			}
849 		}
850 		/* Window scaling. */
851 		if ((flags & TH_SYN) && (tp->t_flags & TF_REQ_SCALE)) {
852 			to.to_wscale = tp->request_r_scale;
853 			to.to_flags |= TOF_SCALE;
854 		}
855 		/* Timestamps. */
856 		if ((tp->t_flags & TF_RCVD_TSTMP) ||
857 		    ((flags & TH_SYN) && (tp->t_flags & TF_REQ_TSTMP))) {
858 			curticks = tcp_ts_getticks();
859 			to.to_tsval = curticks + tp->ts_offset;
860 			to.to_tsecr = tp->ts_recent;
861 			to.to_flags |= TOF_TS;
862 			if (tp->t_rxtshift == 1)
863 				tp->t_badrxtwin = curticks;
864 		}
865 
866 		/* Set receive buffer autosizing timestamp. */
867 		if (tp->rfbuf_ts == 0 &&
868 		    (so->so_rcv.sb_flags & SB_AUTOSIZE))
869 			tp->rfbuf_ts = tcp_ts_getticks();
870 
871 		/* Selective ACK's. */
872 		if (tp->t_flags & TF_SACK_PERMIT) {
873 			if (flags & TH_SYN)
874 				to.to_flags |= TOF_SACKPERM;
875 			else if (TCPS_HAVEESTABLISHED(tp->t_state) &&
876 			    tp->rcv_numsacks > 0) {
877 				to.to_flags |= TOF_SACK;
878 				to.to_nsacks = tp->rcv_numsacks;
879 				to.to_sacks = (u_char *)tp->sackblks;
880 			}
881 		}
882 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
883 		/* TCP-MD5 (RFC2385). */
884 		/*
885 		 * Check that TCP_MD5SIG is enabled in tcpcb to
886 		 * account the size needed to set this TCP option.
887 		 */
888 		if (tp->t_flags & TF_SIGNATURE)
889 			to.to_flags |= TOF_SIGNATURE;
890 #endif /* TCP_SIGNATURE */
891 
892 		/* Processing the options. */
893 		hdrlen += optlen = tcp_addoptions(&to, opt);
894 		/*
895 		 * If we wanted a TFO option to be added, but it was unable
896 		 * to fit, ensure no data is sent.
897 		 */
898 		if (IS_FASTOPEN(tp->t_flags) && wanted_cookie &&
899 		    !(to.to_flags & TOF_FASTOPEN))
900 			len = 0;
901 	}
902 	if (tp->t_port) {
903 		if (V_tcp_udp_tunneling_port == 0) {
904 			/* The port was removed?? */
905 			SOCKBUF_UNLOCK(&so->so_snd);
906 			return (EHOSTUNREACH);
907 		}
908 		hdrlen += sizeof(struct udphdr);
909 	}
910 	/*
911 	 * Adjust data length if insertion of options will
912 	 * bump the packet length beyond the t_maxseg length.
913 	 * Clear the FIN bit because we cut off the tail of
914 	 * the segment.
915 	 */
916 	if (len + optlen + ipoptlen > tp->t_maxseg) {
917 		flags &= ~TH_FIN;
918 
919 		if (tso) {
920 			u_int if_hw_tsomax;
921 			u_int moff;
922 			int max_len;
923 
924 			/* extract TSO information */
925 			if_hw_tsomax = tp->t_tsomax;
926 			if_hw_tsomaxsegcount = tp->t_tsomaxsegcount;
927 			if_hw_tsomaxsegsize = tp->t_tsomaxsegsize;
928 
929 			/*
930 			 * Limit a TSO burst to prevent it from
931 			 * overflowing or exceeding the maximum length
932 			 * allowed by the network interface:
933 			 */
934 			KASSERT(ipoptlen == 0,
935 			    ("%s: TSO can't do IP options", __func__));
936 
937 			/*
938 			 * Check if we should limit by maximum payload
939 			 * length:
940 			 */
941 			if (if_hw_tsomax != 0) {
942 				/* compute maximum TSO length */
943 				max_len = (if_hw_tsomax - hdrlen -
944 				    max_linkhdr);
945 				if (max_len <= 0) {
946 					len = 0;
947 				} else if (len > max_len) {
948 					sendalot = 1;
949 					len = max_len;
950 				}
951 			}
952 
953 			/*
954 			 * Prevent the last segment from being
955 			 * fractional unless the send sockbuf can be
956 			 * emptied:
957 			 */
958 			max_len = (tp->t_maxseg - optlen);
959 			if (((uint32_t)off + (uint32_t)len) <
960 			    sbavail(&so->so_snd)) {
961 				moff = len % max_len;
962 				if (moff != 0) {
963 					len -= moff;
964 					sendalot = 1;
965 				}
966 			}
967 
968 			/*
969 			 * In case there are too many small fragments
970 			 * don't use TSO:
971 			 */
972 			if (len <= max_len) {
973 				len = max_len;
974 				sendalot = 1;
975 				tso = 0;
976 			}
977 
978 			/*
979 			 * Send the FIN in a separate segment
980 			 * after the bulk sending is done.
981 			 * We don't trust the TSO implementations
982 			 * to clear the FIN flag on all but the
983 			 * last segment.
984 			 */
985 			if (tp->t_flags & TF_NEEDFIN)
986 				sendalot = 1;
987 		} else {
988 			if (optlen + ipoptlen >= tp->t_maxseg) {
989 				/*
990 				 * Since we don't have enough space to put
991 				 * the IP header chain and the TCP header in
992 				 * one packet as required by RFC 7112, don't
993 				 * send it. Also ensure that at least one
994 				 * byte of the payload can be put into the
995 				 * TCP segment.
996 				 */
997 				SOCKBUF_UNLOCK(&so->so_snd);
998 				error = EMSGSIZE;
999 				sack_rxmit = 0;
1000 				goto out;
1001 			}
1002 			len = tp->t_maxseg - optlen - ipoptlen;
1003 			sendalot = 1;
1004 			if (dont_sendalot)
1005 				sendalot = 0;
1006 		}
1007 	} else
1008 		tso = 0;
1009 
1010 	KASSERT(len + hdrlen + ipoptlen <= IP_MAXPACKET,
1011 	    ("%s: len > IP_MAXPACKET", __func__));
1012 
1013 /*#ifdef DIAGNOSTIC*/
1014 #ifdef INET6
1015 	if (max_linkhdr + hdrlen > MCLBYTES)
1016 #else
1017 	if (max_linkhdr + hdrlen > MHLEN)
1018 #endif
1019 		panic("tcphdr too big");
1020 /*#endif*/
1021 
1022 	/*
1023 	 * This KASSERT is here to catch edge cases at a well defined place.
1024 	 * Before, those had triggered (random) panic conditions further down.
1025 	 */
1026 	KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
1027 
1028 	/*
1029 	 * Grab a header mbuf, attaching a copy of data to
1030 	 * be transmitted, and initialize the header from
1031 	 * the template for sends on this connection.
1032 	 */
1033 	if (len) {
1034 		struct mbuf *mb;
1035 		struct sockbuf *msb;
1036 		u_int moff;
1037 
1038 		if ((tp->t_flags & TF_FORCEDATA) && len == 1) {
1039 			TCPSTAT_INC(tcps_sndprobe);
1040 #ifdef STATS
1041 			if (SEQ_LT(tp->snd_nxt, tp->snd_max))
1042 				stats_voi_update_abs_u32(tp->t_stats,
1043 				VOI_TCP_RETXPB, len);
1044 			else
1045 				stats_voi_update_abs_u64(tp->t_stats,
1046 				    VOI_TCP_TXPB, len);
1047 #endif /* STATS */
1048 		} else if (SEQ_LT(tp->snd_nxt, tp->snd_max) || sack_rxmit) {
1049 			tp->t_sndrexmitpack++;
1050 			TCPSTAT_INC(tcps_sndrexmitpack);
1051 			TCPSTAT_ADD(tcps_sndrexmitbyte, len);
1052 #ifdef STATS
1053 			stats_voi_update_abs_u32(tp->t_stats, VOI_TCP_RETXPB,
1054 			    len);
1055 #endif /* STATS */
1056 		} else {
1057 			TCPSTAT_INC(tcps_sndpack);
1058 			TCPSTAT_ADD(tcps_sndbyte, len);
1059 #ifdef STATS
1060 			stats_voi_update_abs_u64(tp->t_stats, VOI_TCP_TXPB,
1061 			    len);
1062 #endif /* STATS */
1063 		}
1064 #ifdef INET6
1065 		if (MHLEN < hdrlen + max_linkhdr)
1066 			m = m_getcl(M_NOWAIT, MT_DATA, M_PKTHDR);
1067 		else
1068 #endif
1069 			m = m_gethdr(M_NOWAIT, MT_DATA);
1070 
1071 		if (m == NULL) {
1072 			SOCKBUF_UNLOCK(&so->so_snd);
1073 			error = ENOBUFS;
1074 			sack_rxmit = 0;
1075 			goto out;
1076 		}
1077 
1078 		m->m_data += max_linkhdr;
1079 		m->m_len = hdrlen;
1080 
1081 		/*
1082 		 * Start the m_copy functions from the closest mbuf
1083 		 * to the offset in the socket buffer chain.
1084 		 */
1085 		mb = sbsndptr_noadv(&so->so_snd, off, &moff);
1086 		if (len <= MHLEN - hdrlen - max_linkhdr && !hw_tls) {
1087 			m_copydata(mb, moff, len,
1088 			    mtod(m, caddr_t) + hdrlen);
1089 			if (SEQ_LT(tp->snd_nxt, tp->snd_max))
1090 				sbsndptr_adv(&so->so_snd, mb, len);
1091 			m->m_len += len;
1092 		} else {
1093 			if (SEQ_LT(tp->snd_nxt, tp->snd_max))
1094 				msb = NULL;
1095 			else
1096 				msb = &so->so_snd;
1097 			m->m_next = tcp_m_copym(mb, moff,
1098 			    &len, if_hw_tsomaxsegcount,
1099 			    if_hw_tsomaxsegsize, msb, hw_tls);
1100 			if (len <= (tp->t_maxseg - optlen)) {
1101 				/*
1102 				 * Must have ran out of mbufs for the copy
1103 				 * shorten it to no longer need tso. Lets
1104 				 * not put on sendalot since we are low on
1105 				 * mbufs.
1106 				 */
1107 				tso = 0;
1108 			}
1109 			if (m->m_next == NULL) {
1110 				SOCKBUF_UNLOCK(&so->so_snd);
1111 				(void) m_free(m);
1112 				error = ENOBUFS;
1113 				sack_rxmit = 0;
1114 				goto out;
1115 			}
1116 		}
1117 
1118 		/*
1119 		 * If we're sending everything we've got, set PUSH.
1120 		 * (This will keep happy those implementations which only
1121 		 * give data to the user when a buffer fills or
1122 		 * a PUSH comes in.)
1123 		 */
1124 		if (((uint32_t)off + (uint32_t)len == sbused(&so->so_snd)) &&
1125 		    !(flags & TH_SYN))
1126 			flags |= TH_PUSH;
1127 		SOCKBUF_UNLOCK(&so->so_snd);
1128 	} else {
1129 		SOCKBUF_UNLOCK(&so->so_snd);
1130 		if (tp->t_flags & TF_ACKNOW)
1131 			TCPSTAT_INC(tcps_sndacks);
1132 		else if (flags & (TH_SYN|TH_FIN|TH_RST))
1133 			TCPSTAT_INC(tcps_sndctrl);
1134 		else if (SEQ_GT(tp->snd_up, tp->snd_una))
1135 			TCPSTAT_INC(tcps_sndurg);
1136 		else
1137 			TCPSTAT_INC(tcps_sndwinup);
1138 
1139 		m = m_gethdr(M_NOWAIT, MT_DATA);
1140 		if (m == NULL) {
1141 			error = ENOBUFS;
1142 			sack_rxmit = 0;
1143 			goto out;
1144 		}
1145 #ifdef INET6
1146 		if (isipv6 && (MHLEN < hdrlen + max_linkhdr) &&
1147 		    MHLEN >= hdrlen) {
1148 			M_ALIGN(m, hdrlen);
1149 		} else
1150 #endif
1151 		m->m_data += max_linkhdr;
1152 		m->m_len = hdrlen;
1153 	}
1154 	SOCKBUF_UNLOCK_ASSERT(&so->so_snd);
1155 	m->m_pkthdr.rcvif = (struct ifnet *)0;
1156 #ifdef MAC
1157 	mac_inpcb_create_mbuf(tp->t_inpcb, m);
1158 #endif
1159 #ifdef INET6
1160 	if (isipv6) {
1161 		ip6 = mtod(m, struct ip6_hdr *);
1162 		if (tp->t_port) {
1163 			udp = (struct udphdr *)((caddr_t)ip6 + sizeof(struct ip6_hdr));
1164 			udp->uh_sport = htons(V_tcp_udp_tunneling_port);
1165 			udp->uh_dport = tp->t_port;
1166 			ulen = hdrlen + len - sizeof(struct ip6_hdr);
1167 			udp->uh_ulen = htons(ulen);
1168 			th = (struct tcphdr *)(udp + 1);
1169 		} else {
1170 			th = (struct tcphdr *)(ip6 + 1);
1171 		}
1172 		tcpip_fillheaders(tp->t_inpcb, tp->t_port, ip6, th);
1173 	} else
1174 #endif /* INET6 */
1175 	{
1176 		ip = mtod(m, struct ip *);
1177 #ifdef TCPDEBUG
1178 		ipov = (struct ipovly *)ip;
1179 #endif
1180 		if (tp->t_port) {
1181 			udp = (struct udphdr *)((caddr_t)ip + sizeof(struct ip));
1182 			udp->uh_sport = htons(V_tcp_udp_tunneling_port);
1183 			udp->uh_dport = tp->t_port;
1184 			ulen = hdrlen + len - sizeof(struct ip);
1185 			udp->uh_ulen = htons(ulen);
1186 			th = (struct tcphdr *)(udp + 1);
1187 		} else
1188 			th = (struct tcphdr *)(ip + 1);
1189 		tcpip_fillheaders(tp->t_inpcb, tp->t_port, ip, th);
1190 	}
1191 
1192 	/*
1193 	 * Fill in fields, remembering maximum advertised
1194 	 * window for use in delaying messages about window sizes.
1195 	 * If resending a FIN, be sure not to use a new sequence number.
1196 	 */
1197 	if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
1198 	    tp->snd_nxt == tp->snd_max)
1199 		tp->snd_nxt--;
1200 	/*
1201 	 * If we are starting a connection, send ECN setup
1202 	 * SYN packet. If we are on a retransmit, we may
1203 	 * resend those bits a number of times as per
1204 	 * RFC 3168.
1205 	 */
1206 	if (tp->t_state == TCPS_SYN_SENT && V_tcp_do_ecn) {
1207 		flags |= tcp_ecn_output_syn_sent(tp);
1208 	}
1209 	/* Also handle parallel SYN for ECN */
1210 	if ((TCPS_HAVERCVDSYN(tp->t_state)) &&
1211 	    (tp->t_flags2 & TF2_ECN_PERMIT)) {
1212 		int ect = tcp_ecn_output_established(tp, &flags, len, sack_rxmit);
1213 		if ((tp->t_state == TCPS_SYN_RECEIVED) &&
1214 		    (tp->t_flags2 & TF2_ECN_SND_ECE))
1215 			tp->t_flags2 &= ~TF2_ECN_SND_ECE;
1216 #ifdef INET6
1217 		if (isipv6) {
1218 			ip6->ip6_flow &= ~htonl(IPTOS_ECN_MASK << 20);
1219 			ip6->ip6_flow |= htonl(ect << 20);
1220 		}
1221 		else
1222 #endif
1223 		{
1224 			ip->ip_tos &= ~IPTOS_ECN_MASK;
1225 			ip->ip_tos |= ect;
1226 		}
1227 	}
1228 
1229 	/*
1230 	 * If we are doing retransmissions, then snd_nxt will
1231 	 * not reflect the first unsent octet.  For ACK only
1232 	 * packets, we do not want the sequence number of the
1233 	 * retransmitted packet, we want the sequence number
1234 	 * of the next unsent octet.  So, if there is no data
1235 	 * (and no SYN or FIN), use snd_max instead of snd_nxt
1236 	 * when filling in ti_seq.  But if we are in persist
1237 	 * state, snd_max might reflect one byte beyond the
1238 	 * right edge of the window, so use snd_nxt in that
1239 	 * case, since we know we aren't doing a retransmission.
1240 	 * (retransmit and persist are mutually exclusive...)
1241 	 */
1242 	if (sack_rxmit == 0) {
1243 		if (len || (flags & (TH_SYN|TH_FIN)) ||
1244 		    tcp_timer_active(tp, TT_PERSIST))
1245 			th->th_seq = htonl(tp->snd_nxt);
1246 		else
1247 			th->th_seq = htonl(tp->snd_max);
1248 	} else {
1249 		th->th_seq = htonl(p->rxmit);
1250 		p->rxmit += len;
1251 		/*
1252 		 * Lost Retransmission Detection
1253 		 * trigger resending of a (then
1254 		 * still existing) hole, when
1255 		 * fack acks recoverypoint.
1256 		 */
1257 		if ((tp->t_flags & TF_LRD) && SEQ_GEQ(p->rxmit, p->end))
1258 			p->rxmit = tp->snd_recover;
1259 		tp->sackhint.sack_bytes_rexmit += len;
1260 	}
1261 	if (IN_RECOVERY(tp->t_flags)) {
1262 		/*
1263 		 * Account all bytes transmitted while
1264 		 * IN_RECOVERY, simplifying PRR and
1265 		 * Lost Retransmit Detection
1266 		 */
1267 		tp->sackhint.prr_out += len;
1268 	}
1269 	th->th_ack = htonl(tp->rcv_nxt);
1270 	if (optlen) {
1271 		bcopy(opt, th + 1, optlen);
1272 		th->th_off = (sizeof (struct tcphdr) + optlen) >> 2;
1273 	}
1274 	tcp_set_flags(th, flags);
1275 	/*
1276 	 * Calculate receive window.  Don't shrink window,
1277 	 * but avoid silly window syndrome.
1278 	 * If a RST segment is sent, advertise a window of zero.
1279 	 */
1280 	if (flags & TH_RST) {
1281 		recwin = 0;
1282 	} else {
1283 		if (recwin < (so->so_rcv.sb_hiwat / 4) &&
1284 		    recwin < tp->t_maxseg)
1285 			recwin = 0;
1286 		if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt) &&
1287 		    recwin < (tp->rcv_adv - tp->rcv_nxt))
1288 			recwin = (tp->rcv_adv - tp->rcv_nxt);
1289 	}
1290 	/*
1291 	 * According to RFC1323 the window field in a SYN (i.e., a <SYN>
1292 	 * or <SYN,ACK>) segment itself is never scaled.  The <SYN,ACK>
1293 	 * case is handled in syncache.
1294 	 */
1295 	if (flags & TH_SYN)
1296 		th->th_win = htons((u_short)
1297 				(min(sbspace(&so->so_rcv), TCP_MAXWIN)));
1298 	else {
1299 		/* Avoid shrinking window with window scaling. */
1300 		recwin = roundup2(recwin, 1 << tp->rcv_scale);
1301 		th->th_win = htons((u_short)(recwin >> tp->rcv_scale));
1302 	}
1303 
1304 	/*
1305 	 * Adjust the RXWIN0SENT flag - indicate that we have advertised
1306 	 * a 0 window.  This may cause the remote transmitter to stall.  This
1307 	 * flag tells soreceive() to disable delayed acknowledgements when
1308 	 * draining the buffer.  This can occur if the receiver is attempting
1309 	 * to read more data than can be buffered prior to transmitting on
1310 	 * the connection.
1311 	 */
1312 	if (th->th_win == 0) {
1313 		tp->t_sndzerowin++;
1314 		tp->t_flags |= TF_RXWIN0SENT;
1315 	} else
1316 		tp->t_flags &= ~TF_RXWIN0SENT;
1317 	if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
1318 		th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
1319 		th->th_flags |= TH_URG;
1320 	} else
1321 		/*
1322 		 * If no urgent pointer to send, then we pull
1323 		 * the urgent pointer to the left edge of the send window
1324 		 * so that it doesn't drift into the send window on sequence
1325 		 * number wraparound.
1326 		 */
1327 		tp->snd_up = tp->snd_una;		/* drag it along */
1328 
1329 	/*
1330 	 * Put TCP length in extended header, and then
1331 	 * checksum extended header and data.
1332 	 */
1333 	m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
1334 
1335 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1336 	if (to.to_flags & TOF_SIGNATURE) {
1337 		/*
1338 		 * Calculate MD5 signature and put it into the place
1339 		 * determined before.
1340 		 * NOTE: since TCP options buffer doesn't point into
1341 		 * mbuf's data, calculate offset and use it.
1342 		 */
1343 		if (!TCPMD5_ENABLED() || (error = TCPMD5_OUTPUT(m, th,
1344 		    (u_char *)(th + 1) + (to.to_signature - opt))) != 0) {
1345 			/*
1346 			 * Do not send segment if the calculation of MD5
1347 			 * digest has failed.
1348 			 */
1349 			m_freem(m);
1350 			goto out;
1351 		}
1352 	}
1353 #endif
1354 #ifdef INET6
1355 	if (isipv6) {
1356 		/*
1357 		 * There is no need to fill in ip6_plen right now.
1358 		 * It will be filled later by ip6_output.
1359 		 */
1360 		if (tp->t_port) {
1361 			m->m_pkthdr.csum_flags = CSUM_UDP_IPV6;
1362 			m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
1363 			udp->uh_sum = in6_cksum_pseudo(ip6, ulen, IPPROTO_UDP, 0);
1364 			th->th_sum = htons(0);
1365 			UDPSTAT_INC(udps_opackets);
1366 		} else {
1367 			m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
1368 			m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1369 			th->th_sum = in6_cksum_pseudo(ip6,
1370 			    sizeof(struct tcphdr) + optlen + len, IPPROTO_TCP,
1371 			    0);
1372 		}
1373 	}
1374 #endif
1375 #if defined(INET6) && defined(INET)
1376 	else
1377 #endif
1378 #ifdef INET
1379 	{
1380 		if (tp->t_port) {
1381 			m->m_pkthdr.csum_flags = CSUM_UDP;
1382 			m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
1383 			udp->uh_sum = in_pseudo(ip->ip_src.s_addr,
1384 			   ip->ip_dst.s_addr, htons(ulen + IPPROTO_UDP));
1385 			th->th_sum = htons(0);
1386 			UDPSTAT_INC(udps_opackets);
1387 		} else {
1388 			m->m_pkthdr.csum_flags = CSUM_TCP;
1389 			m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1390 			th->th_sum = in_pseudo(ip->ip_src.s_addr,
1391 			    ip->ip_dst.s_addr, htons(sizeof(struct tcphdr) +
1392 			    IPPROTO_TCP + len + optlen));
1393 		}
1394 
1395 		/* IP version must be set here for ipv4/ipv6 checking later */
1396 		KASSERT(ip->ip_v == IPVERSION,
1397 		    ("%s: IP version incorrect: %d", __func__, ip->ip_v));
1398 	}
1399 #endif
1400 
1401 	/*
1402 	 * Enable TSO and specify the size of the segments.
1403 	 * The TCP pseudo header checksum is always provided.
1404 	 */
1405 	if (tso) {
1406 		KASSERT(len > tp->t_maxseg - optlen,
1407 		    ("%s: len <= tso_segsz", __func__));
1408 		m->m_pkthdr.csum_flags |= CSUM_TSO;
1409 		m->m_pkthdr.tso_segsz = tp->t_maxseg - optlen;
1410 	}
1411 
1412 	KASSERT(len + hdrlen == m_length(m, NULL),
1413 	    ("%s: mbuf chain shorter than expected: %d + %u != %u",
1414 	    __func__, len, hdrlen, m_length(m, NULL)));
1415 
1416 #ifdef TCP_HHOOK
1417 	/* Run HHOOK_TCP_ESTABLISHED_OUT helper hooks. */
1418 	hhook_run_tcp_est_out(tp, th, &to, len, tso);
1419 #endif
1420 
1421 #ifdef TCPDEBUG
1422 	/*
1423 	 * Trace.
1424 	 */
1425 	if (so->so_options & SO_DEBUG) {
1426 		u_short save = 0;
1427 #ifdef INET6
1428 		if (!isipv6)
1429 #endif
1430 		{
1431 			save = ipov->ih_len;
1432 			ipov->ih_len = htons(m->m_pkthdr.len /* - hdrlen + (th->th_off << 2) */);
1433 		}
1434 		tcp_trace(TA_OUTPUT, tp->t_state, tp, mtod(m, void *), th, 0);
1435 #ifdef INET6
1436 		if (!isipv6)
1437 #endif
1438 		ipov->ih_len = save;
1439 	}
1440 #endif /* TCPDEBUG */
1441 	TCP_PROBE3(debug__output, tp, th, m);
1442 
1443 	/* We're getting ready to send; log now. */
1444 	TCP_LOG_EVENT(tp, th, &so->so_rcv, &so->so_snd, TCP_LOG_OUT, ERRNO_UNK,
1445 	    len, NULL, false);
1446 
1447 	/*
1448 	 * Fill in IP length and desired time to live and
1449 	 * send to IP level.  There should be a better way
1450 	 * to handle ttl and tos; we could keep them in
1451 	 * the template, but need a way to checksum without them.
1452 	 */
1453 	/*
1454 	 * m->m_pkthdr.len should have been set before checksum calculation,
1455 	 * because in6_cksum() need it.
1456 	 */
1457 #ifdef INET6
1458 	if (isipv6) {
1459 		/*
1460 		 * we separately set hoplimit for every segment, since the
1461 		 * user might want to change the value via setsockopt.
1462 		 * Also, desired default hop limit might be changed via
1463 		 * Neighbor Discovery.
1464 		 */
1465 		ip6->ip6_hlim = in6_selecthlim(tp->t_inpcb, NULL);
1466 
1467 		/*
1468 		 * Set the packet size here for the benefit of DTrace probes.
1469 		 * ip6_output() will set it properly; it's supposed to include
1470 		 * the option header lengths as well.
1471 		 */
1472 		ip6->ip6_plen = htons(m->m_pkthdr.len - sizeof(*ip6));
1473 
1474 		if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss)
1475 			tp->t_flags2 |= TF2_PLPMTU_PMTUD;
1476 		else
1477 			tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
1478 
1479 		if (tp->t_state == TCPS_SYN_SENT)
1480 			TCP_PROBE5(connect__request, NULL, tp, ip6, tp, th);
1481 
1482 		TCP_PROBE5(send, NULL, tp, ip6, tp, th);
1483 
1484 #ifdef TCPPCAP
1485 		/* Save packet, if requested. */
1486 		tcp_pcap_add(th, m, &(tp->t_outpkts));
1487 #endif
1488 
1489 		/* TODO: IPv6 IP6TOS_ECT bit on */
1490 		error = ip6_output(m, tp->t_inpcb->in6p_outputopts,
1491 		    &tp->t_inpcb->inp_route6,
1492 		    ((so->so_options & SO_DONTROUTE) ?  IP_ROUTETOIF : 0),
1493 		    NULL, NULL, tp->t_inpcb);
1494 
1495 		if (error == EMSGSIZE && tp->t_inpcb->inp_route6.ro_nh != NULL)
1496 			mtu = tp->t_inpcb->inp_route6.ro_nh->nh_mtu;
1497 	}
1498 #endif /* INET6 */
1499 #if defined(INET) && defined(INET6)
1500 	else
1501 #endif
1502 #ifdef INET
1503     {
1504 	ip->ip_len = htons(m->m_pkthdr.len);
1505 #ifdef INET6
1506 	if (tp->t_inpcb->inp_vflag & INP_IPV6PROTO)
1507 		ip->ip_ttl = in6_selecthlim(tp->t_inpcb, NULL);
1508 #endif /* INET6 */
1509 	/*
1510 	 * If we do path MTU discovery, then we set DF on every packet.
1511 	 * This might not be the best thing to do according to RFC3390
1512 	 * Section 2. However the tcp hostcache migitates the problem
1513 	 * so it affects only the first tcp connection with a host.
1514 	 *
1515 	 * NB: Don't set DF on small MTU/MSS to have a safe fallback.
1516 	 */
1517 	if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss) {
1518 		tp->t_flags2 |= TF2_PLPMTU_PMTUD;
1519 		if (tp->t_port == 0 || len < V_tcp_minmss) {
1520 			ip->ip_off |= htons(IP_DF);
1521 		}
1522 	} else {
1523 		tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
1524 	}
1525 
1526 	if (tp->t_state == TCPS_SYN_SENT)
1527 		TCP_PROBE5(connect__request, NULL, tp, ip, tp, th);
1528 
1529 	TCP_PROBE5(send, NULL, tp, ip, tp, th);
1530 
1531 #ifdef TCPPCAP
1532 	/* Save packet, if requested. */
1533 	tcp_pcap_add(th, m, &(tp->t_outpkts));
1534 #endif
1535 
1536 	error = ip_output(m, tp->t_inpcb->inp_options, &tp->t_inpcb->inp_route,
1537 	    ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0), 0,
1538 	    tp->t_inpcb);
1539 
1540 	if (error == EMSGSIZE && tp->t_inpcb->inp_route.ro_nh != NULL)
1541 		mtu = tp->t_inpcb->inp_route.ro_nh->nh_mtu;
1542     }
1543 #endif /* INET */
1544 
1545 out:
1546 	if (error == 0)
1547 		tcp_account_for_send(tp, len, (tp->snd_nxt != tp->snd_max), 0, hw_tls);
1548 	/*
1549 	 * In transmit state, time the transmission and arrange for
1550 	 * the retransmit.  In persist state, just set snd_max.
1551 	 */
1552 	if ((tp->t_flags & TF_FORCEDATA) == 0 ||
1553 	    !tcp_timer_active(tp, TT_PERSIST)) {
1554 		tcp_seq startseq = tp->snd_nxt;
1555 
1556 		/*
1557 		 * Advance snd_nxt over sequence space of this segment.
1558 		 */
1559 		if (flags & (TH_SYN|TH_FIN)) {
1560 			if (flags & TH_SYN)
1561 				tp->snd_nxt++;
1562 			if (flags & TH_FIN) {
1563 				tp->snd_nxt++;
1564 				tp->t_flags |= TF_SENTFIN;
1565 			}
1566 		}
1567 		if (sack_rxmit)
1568 			goto timer;
1569 		tp->snd_nxt += len;
1570 		if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
1571 			tp->snd_max = tp->snd_nxt;
1572 			/*
1573 			 * Time this transmission if not a retransmission and
1574 			 * not currently timing anything.
1575 			 */
1576 			tp->t_sndtime = ticks;
1577 			if (tp->t_rtttime == 0) {
1578 				tp->t_rtttime = ticks;
1579 				tp->t_rtseq = startseq;
1580 				TCPSTAT_INC(tcps_segstimed);
1581 			}
1582 #ifdef STATS
1583 			if (!(tp->t_flags & TF_GPUTINPROG) && len) {
1584 				tp->t_flags |= TF_GPUTINPROG;
1585 				tp->gput_seq = startseq;
1586 				tp->gput_ack = startseq +
1587 				    ulmin(sbavail(&so->so_snd) - off, sendwin);
1588 				tp->gput_ts = tcp_ts_getticks();
1589 			}
1590 #endif /* STATS */
1591 		}
1592 
1593 		/*
1594 		 * Set retransmit timer if not currently set,
1595 		 * and not doing a pure ack or a keep-alive probe.
1596 		 * Initial value for retransmit timer is smoothed
1597 		 * round-trip time + 2 * round-trip time variance.
1598 		 * Initialize shift counter which is used for backoff
1599 		 * of retransmit time.
1600 		 */
1601 timer:
1602 		if (!tcp_timer_active(tp, TT_REXMT) &&
1603 		    ((sack_rxmit && tp->snd_nxt != tp->snd_max) ||
1604 		     (tp->snd_nxt != tp->snd_una))) {
1605 			if (tcp_timer_active(tp, TT_PERSIST)) {
1606 				tcp_timer_activate(tp, TT_PERSIST, 0);
1607 				tp->t_rxtshift = 0;
1608 			}
1609 			tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
1610 		} else if (len == 0 && sbavail(&so->so_snd) &&
1611 		    !tcp_timer_active(tp, TT_REXMT) &&
1612 		    !tcp_timer_active(tp, TT_PERSIST)) {
1613 			/*
1614 			 * Avoid a situation where we do not set persist timer
1615 			 * after a zero window condition. For example:
1616 			 * 1) A -> B: packet with enough data to fill the window
1617 			 * 2) B -> A: ACK for #1 + new data (0 window
1618 			 *    advertisement)
1619 			 * 3) A -> B: ACK for #2, 0 len packet
1620 			 *
1621 			 * In this case, A will not activate the persist timer,
1622 			 * because it chose to send a packet. Unless tcp_output
1623 			 * is called for some other reason (delayed ack timer,
1624 			 * another input packet from B, socket syscall), A will
1625 			 * not send zero window probes.
1626 			 *
1627 			 * So, if you send a 0-length packet, but there is data
1628 			 * in the socket buffer, and neither the rexmt or
1629 			 * persist timer is already set, then activate the
1630 			 * persist timer.
1631 			 */
1632 			tp->t_rxtshift = 0;
1633 			tcp_setpersist(tp);
1634 		}
1635 	} else {
1636 		/*
1637 		 * Persist case, update snd_max but since we are in
1638 		 * persist mode (no window) we do not update snd_nxt.
1639 		 */
1640 		int xlen = len;
1641 		if (flags & TH_SYN)
1642 			++xlen;
1643 		if (flags & TH_FIN) {
1644 			++xlen;
1645 			tp->t_flags |= TF_SENTFIN;
1646 		}
1647 		if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
1648 			tp->snd_max = tp->snd_nxt + xlen;
1649 	}
1650 	if ((error == 0) &&
1651 	    (TCPS_HAVEESTABLISHED(tp->t_state) &&
1652 	     (tp->t_flags & TF_SACK_PERMIT) &&
1653 	     tp->rcv_numsacks > 0)) {
1654 		    /* Clean up any DSACK's sent */
1655 		    tcp_clean_dsack_blocks(tp);
1656 	}
1657 	if (error) {
1658 		/* Record the error. */
1659 		TCP_LOG_EVENT(tp, NULL, &so->so_rcv, &so->so_snd, TCP_LOG_OUT,
1660 		    error, 0, NULL, false);
1661 
1662 		/*
1663 		 * We know that the packet was lost, so back out the
1664 		 * sequence number advance, if any.
1665 		 *
1666 		 * If the error is EPERM the packet got blocked by the
1667 		 * local firewall.  Normally we should terminate the
1668 		 * connection but the blocking may have been spurious
1669 		 * due to a firewall reconfiguration cycle.  So we treat
1670 		 * it like a packet loss and let the retransmit timer and
1671 		 * timeouts do their work over time.
1672 		 * XXX: It is a POLA question whether calling tcp_drop right
1673 		 * away would be the really correct behavior instead.
1674 		 */
1675 		if (((tp->t_flags & TF_FORCEDATA) == 0 ||
1676 		    !tcp_timer_active(tp, TT_PERSIST)) &&
1677 		    ((flags & TH_SYN) == 0) &&
1678 		    (error != EPERM)) {
1679 			if (sack_rxmit) {
1680 				p->rxmit -= len;
1681 				tp->sackhint.sack_bytes_rexmit -= len;
1682 				KASSERT(tp->sackhint.sack_bytes_rexmit >= 0,
1683 				    ("sackhint bytes rtx >= 0"));
1684 			} else
1685 				tp->snd_nxt -= len;
1686 		}
1687 		SOCKBUF_UNLOCK_ASSERT(&so->so_snd);	/* Check gotos. */
1688 		switch (error) {
1689 		case EACCES:
1690 		case EPERM:
1691 			tp->t_softerror = error;
1692 			return (error);
1693 		case ENOBUFS:
1694 			TCP_XMIT_TIMER_ASSERT(tp, len, flags);
1695 			tp->snd_cwnd = tp->t_maxseg;
1696 			return (0);
1697 		case EMSGSIZE:
1698 			/*
1699 			 * For some reason the interface we used initially
1700 			 * to send segments changed to another or lowered
1701 			 * its MTU.
1702 			 * If TSO was active we either got an interface
1703 			 * without TSO capabilits or TSO was turned off.
1704 			 * If we obtained mtu from ip_output() then update
1705 			 * it and try again.
1706 			 */
1707 			if (tso)
1708 				tp->t_flags &= ~TF_TSO;
1709 			if (mtu != 0) {
1710 				tcp_mss_update(tp, -1, mtu, NULL, NULL);
1711 				goto again;
1712 			}
1713 			return (error);
1714 		case EHOSTDOWN:
1715 		case EHOSTUNREACH:
1716 		case ENETDOWN:
1717 		case ENETUNREACH:
1718 			if (TCPS_HAVERCVDSYN(tp->t_state)) {
1719 				tp->t_softerror = error;
1720 				return (0);
1721 			}
1722 			/* FALLTHROUGH */
1723 		default:
1724 			return (error);
1725 		}
1726 	}
1727 	TCPSTAT_INC(tcps_sndtotal);
1728 
1729 	/*
1730 	 * Data sent (as far as we can tell).
1731 	 * If this advertises a larger window than any other segment,
1732 	 * then remember the size of the advertised window.
1733 	 * Any pending ACK has now been sent.
1734 	 */
1735 	if (SEQ_GT(tp->rcv_nxt + recwin, tp->rcv_adv))
1736 		tp->rcv_adv = tp->rcv_nxt + recwin;
1737 	tp->last_ack_sent = tp->rcv_nxt;
1738 	tp->t_flags &= ~(TF_ACKNOW | TF_DELACK);
1739 	if (tcp_timer_active(tp, TT_DELACK))
1740 		tcp_timer_activate(tp, TT_DELACK, 0);
1741 #if 0
1742 	/*
1743 	 * This completely breaks TCP if newreno is turned on.  What happens
1744 	 * is that if delayed-acks are turned on on the receiver, this code
1745 	 * on the transmitter effectively destroys the TCP window, forcing
1746 	 * it to four packets (1.5Kx4 = 6K window).
1747 	 */
1748 	if (sendalot && --maxburst)
1749 		goto again;
1750 #endif
1751 	if (sendalot)
1752 		goto again;
1753 	return (0);
1754 }
1755 
1756 void
1757 tcp_setpersist(struct tcpcb *tp)
1758 {
1759 	int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
1760 	int tt;
1761 
1762 	tp->t_flags &= ~TF_PREVVALID;
1763 	if (tcp_timer_active(tp, TT_REXMT))
1764 		panic("tcp_setpersist: retransmit pending");
1765 	/*
1766 	 * Start/restart persistence timer.
1767 	 */
1768 	TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift],
1769 		      tcp_persmin, tcp_persmax);
1770 	tcp_timer_activate(tp, TT_PERSIST, tt);
1771 	if (tp->t_rxtshift < TCP_MAXRXTSHIFT)
1772 		tp->t_rxtshift++;
1773 }
1774 
1775 /*
1776  * Insert TCP options according to the supplied parameters to the place
1777  * optp in a consistent way.  Can handle unaligned destinations.
1778  *
1779  * The order of the option processing is crucial for optimal packing and
1780  * alignment for the scarce option space.
1781  *
1782  * The optimal order for a SYN/SYN-ACK segment is:
1783  *   MSS (4) + NOP (1) + Window scale (3) + SACK permitted (2) +
1784  *   Timestamp (10) + Signature (18) = 38 bytes out of a maximum of 40.
1785  *
1786  * The SACK options should be last.  SACK blocks consume 8*n+2 bytes.
1787  * So a full size SACK blocks option is 34 bytes (with 4 SACK blocks).
1788  * At minimum we need 10 bytes (to generate 1 SACK block).  If both
1789  * TCP Timestamps (12 bytes) and TCP Signatures (18 bytes) are present,
1790  * we only have 10 bytes for SACK options (40 - (12 + 18)).
1791  */
1792 int
1793 tcp_addoptions(struct tcpopt *to, u_char *optp)
1794 {
1795 	u_int32_t mask, optlen = 0;
1796 
1797 	for (mask = 1; mask < TOF_MAXOPT; mask <<= 1) {
1798 		if ((to->to_flags & mask) != mask)
1799 			continue;
1800 		if (optlen == TCP_MAXOLEN)
1801 			break;
1802 		switch (to->to_flags & mask) {
1803 		case TOF_MSS:
1804 			while (optlen % 4) {
1805 				optlen += TCPOLEN_NOP;
1806 				*optp++ = TCPOPT_NOP;
1807 			}
1808 			if (TCP_MAXOLEN - optlen < TCPOLEN_MAXSEG)
1809 				continue;
1810 			optlen += TCPOLEN_MAXSEG;
1811 			*optp++ = TCPOPT_MAXSEG;
1812 			*optp++ = TCPOLEN_MAXSEG;
1813 			to->to_mss = htons(to->to_mss);
1814 			bcopy((u_char *)&to->to_mss, optp, sizeof(to->to_mss));
1815 			optp += sizeof(to->to_mss);
1816 			break;
1817 		case TOF_SCALE:
1818 			while (!optlen || optlen % 2 != 1) {
1819 				optlen += TCPOLEN_NOP;
1820 				*optp++ = TCPOPT_NOP;
1821 			}
1822 			if (TCP_MAXOLEN - optlen < TCPOLEN_WINDOW)
1823 				continue;
1824 			optlen += TCPOLEN_WINDOW;
1825 			*optp++ = TCPOPT_WINDOW;
1826 			*optp++ = TCPOLEN_WINDOW;
1827 			*optp++ = to->to_wscale;
1828 			break;
1829 		case TOF_SACKPERM:
1830 			while (optlen % 2) {
1831 				optlen += TCPOLEN_NOP;
1832 				*optp++ = TCPOPT_NOP;
1833 			}
1834 			if (TCP_MAXOLEN - optlen < TCPOLEN_SACK_PERMITTED)
1835 				continue;
1836 			optlen += TCPOLEN_SACK_PERMITTED;
1837 			*optp++ = TCPOPT_SACK_PERMITTED;
1838 			*optp++ = TCPOLEN_SACK_PERMITTED;
1839 			break;
1840 		case TOF_TS:
1841 			while (!optlen || optlen % 4 != 2) {
1842 				optlen += TCPOLEN_NOP;
1843 				*optp++ = TCPOPT_NOP;
1844 			}
1845 			if (TCP_MAXOLEN - optlen < TCPOLEN_TIMESTAMP)
1846 				continue;
1847 			optlen += TCPOLEN_TIMESTAMP;
1848 			*optp++ = TCPOPT_TIMESTAMP;
1849 			*optp++ = TCPOLEN_TIMESTAMP;
1850 			to->to_tsval = htonl(to->to_tsval);
1851 			to->to_tsecr = htonl(to->to_tsecr);
1852 			bcopy((u_char *)&to->to_tsval, optp, sizeof(to->to_tsval));
1853 			optp += sizeof(to->to_tsval);
1854 			bcopy((u_char *)&to->to_tsecr, optp, sizeof(to->to_tsecr));
1855 			optp += sizeof(to->to_tsecr);
1856 			break;
1857 		case TOF_SIGNATURE:
1858 			{
1859 			int siglen = TCPOLEN_SIGNATURE - 2;
1860 
1861 			while (!optlen || optlen % 4 != 2) {
1862 				optlen += TCPOLEN_NOP;
1863 				*optp++ = TCPOPT_NOP;
1864 			}
1865 			if (TCP_MAXOLEN - optlen < TCPOLEN_SIGNATURE) {
1866 				to->to_flags &= ~TOF_SIGNATURE;
1867 				continue;
1868 			}
1869 			optlen += TCPOLEN_SIGNATURE;
1870 			*optp++ = TCPOPT_SIGNATURE;
1871 			*optp++ = TCPOLEN_SIGNATURE;
1872 			to->to_signature = optp;
1873 			while (siglen--)
1874 				 *optp++ = 0;
1875 			break;
1876 			}
1877 		case TOF_SACK:
1878 			{
1879 			int sackblks = 0;
1880 			struct sackblk *sack = (struct sackblk *)to->to_sacks;
1881 			tcp_seq sack_seq;
1882 
1883 			while (!optlen || optlen % 4 != 2) {
1884 				optlen += TCPOLEN_NOP;
1885 				*optp++ = TCPOPT_NOP;
1886 			}
1887 			if (TCP_MAXOLEN - optlen < TCPOLEN_SACKHDR + TCPOLEN_SACK)
1888 				continue;
1889 			optlen += TCPOLEN_SACKHDR;
1890 			*optp++ = TCPOPT_SACK;
1891 			sackblks = min(to->to_nsacks,
1892 					(TCP_MAXOLEN - optlen) / TCPOLEN_SACK);
1893 			*optp++ = TCPOLEN_SACKHDR + sackblks * TCPOLEN_SACK;
1894 			while (sackblks--) {
1895 				sack_seq = htonl(sack->start);
1896 				bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1897 				optp += sizeof(sack_seq);
1898 				sack_seq = htonl(sack->end);
1899 				bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1900 				optp += sizeof(sack_seq);
1901 				optlen += TCPOLEN_SACK;
1902 				sack++;
1903 			}
1904 			TCPSTAT_INC(tcps_sack_send_blocks);
1905 			break;
1906 			}
1907 		case TOF_FASTOPEN:
1908 			{
1909 			int total_len;
1910 
1911 			/* XXX is there any point to aligning this option? */
1912 			total_len = TCPOLEN_FAST_OPEN_EMPTY + to->to_tfo_len;
1913 			if (TCP_MAXOLEN - optlen < total_len) {
1914 				to->to_flags &= ~TOF_FASTOPEN;
1915 				continue;
1916 			}
1917 			*optp++ = TCPOPT_FAST_OPEN;
1918 			*optp++ = total_len;
1919 			if (to->to_tfo_len > 0) {
1920 				bcopy(to->to_tfo_cookie, optp, to->to_tfo_len);
1921 				optp += to->to_tfo_len;
1922 			}
1923 			optlen += total_len;
1924 			break;
1925 			}
1926 		default:
1927 			panic("%s: unknown TCP option type", __func__);
1928 			break;
1929 		}
1930 	}
1931 
1932 	/* Terminate and pad TCP options to a 4 byte boundary. */
1933 	if (optlen % 4) {
1934 		optlen += TCPOLEN_EOL;
1935 		*optp++ = TCPOPT_EOL;
1936 	}
1937 	/*
1938 	 * According to RFC 793 (STD0007):
1939 	 *   "The content of the header beyond the End-of-Option option
1940 	 *    must be header padding (i.e., zero)."
1941 	 *   and later: "The padding is composed of zeros."
1942 	 */
1943 	while (optlen % 4) {
1944 		optlen += TCPOLEN_PAD;
1945 		*optp++ = TCPOPT_PAD;
1946 	}
1947 
1948 	KASSERT(optlen <= TCP_MAXOLEN, ("%s: TCP options too long", __func__));
1949 	return (optlen);
1950 }
1951 
1952 /*
1953  * This is a copy of m_copym(), taking the TSO segment size/limit
1954  * constraints into account, and advancing the sndptr as it goes.
1955  */
1956 struct mbuf *
1957 tcp_m_copym(struct mbuf *m, int32_t off0, int32_t *plen,
1958     int32_t seglimit, int32_t segsize, struct sockbuf *sb, bool hw_tls)
1959 {
1960 #ifdef KERN_TLS
1961 	struct ktls_session *tls, *ntls;
1962 	struct mbuf *start __diagused;
1963 #endif
1964 	struct mbuf *n, **np;
1965 	struct mbuf *top;
1966 	int32_t off = off0;
1967 	int32_t len = *plen;
1968 	int32_t fragsize;
1969 	int32_t len_cp = 0;
1970 	int32_t *pkthdrlen;
1971 	uint32_t mlen, frags;
1972 	bool copyhdr;
1973 
1974 	KASSERT(off >= 0, ("tcp_m_copym, negative off %d", off));
1975 	KASSERT(len >= 0, ("tcp_m_copym, negative len %d", len));
1976 	if (off == 0 && m->m_flags & M_PKTHDR)
1977 		copyhdr = true;
1978 	else
1979 		copyhdr = false;
1980 	while (off > 0) {
1981 		KASSERT(m != NULL, ("tcp_m_copym, offset > size of mbuf chain"));
1982 		if (off < m->m_len)
1983 			break;
1984 		off -= m->m_len;
1985 		if ((sb) && (m == sb->sb_sndptr)) {
1986 			sb->sb_sndptroff += m->m_len;
1987 			sb->sb_sndptr = m->m_next;
1988 		}
1989 		m = m->m_next;
1990 	}
1991 	np = &top;
1992 	top = NULL;
1993 	pkthdrlen = NULL;
1994 #ifdef KERN_TLS
1995 	if (hw_tls && (m->m_flags & M_EXTPG))
1996 		tls = m->m_epg_tls;
1997 	else
1998 		tls = NULL;
1999 	start = m;
2000 #endif
2001 	while (len > 0) {
2002 		if (m == NULL) {
2003 			KASSERT(len == M_COPYALL,
2004 			    ("tcp_m_copym, length > size of mbuf chain"));
2005 			*plen = len_cp;
2006 			if (pkthdrlen != NULL)
2007 				*pkthdrlen = len_cp;
2008 			break;
2009 		}
2010 #ifdef KERN_TLS
2011 		if (hw_tls) {
2012 			if (m->m_flags & M_EXTPG)
2013 				ntls = m->m_epg_tls;
2014 			else
2015 				ntls = NULL;
2016 
2017 			/*
2018 			 * Avoid mixing TLS records with handshake
2019 			 * data or TLS records from different
2020 			 * sessions.
2021 			 */
2022 			if (tls != ntls) {
2023 				MPASS(m != start);
2024 				*plen = len_cp;
2025 				if (pkthdrlen != NULL)
2026 					*pkthdrlen = len_cp;
2027 				break;
2028 			}
2029 		}
2030 #endif
2031 		mlen = min(len, m->m_len - off);
2032 		if (seglimit) {
2033 			/*
2034 			 * For M_EXTPG mbufs, add 3 segments
2035 			 * + 1 in case we are crossing page boundaries
2036 			 * + 2 in case the TLS hdr/trailer are used
2037 			 * It is cheaper to just add the segments
2038 			 * than it is to take the cache miss to look
2039 			 * at the mbuf ext_pgs state in detail.
2040 			 */
2041 			if (m->m_flags & M_EXTPG) {
2042 				fragsize = min(segsize, PAGE_SIZE);
2043 				frags = 3;
2044 			} else {
2045 				fragsize = segsize;
2046 				frags = 0;
2047 			}
2048 
2049 			/* Break if we really can't fit anymore. */
2050 			if ((frags + 1) >= seglimit) {
2051 				*plen =	len_cp;
2052 				if (pkthdrlen != NULL)
2053 					*pkthdrlen = len_cp;
2054 				break;
2055 			}
2056 
2057 			/*
2058 			 * Reduce size if you can't copy the whole
2059 			 * mbuf. If we can't copy the whole mbuf, also
2060 			 * adjust len so the loop will end after this
2061 			 * mbuf.
2062 			 */
2063 			if ((frags + howmany(mlen, fragsize)) >= seglimit) {
2064 				mlen = (seglimit - frags - 1) * fragsize;
2065 				len = mlen;
2066 				*plen = len_cp + len;
2067 				if (pkthdrlen != NULL)
2068 					*pkthdrlen = *plen;
2069 			}
2070 			frags += howmany(mlen, fragsize);
2071 			if (frags == 0)
2072 				frags++;
2073 			seglimit -= frags;
2074 			KASSERT(seglimit > 0,
2075 			    ("%s: seglimit went too low", __func__));
2076 		}
2077 		if (copyhdr)
2078 			n = m_gethdr(M_NOWAIT, m->m_type);
2079 		else
2080 			n = m_get(M_NOWAIT, m->m_type);
2081 		*np = n;
2082 		if (n == NULL)
2083 			goto nospace;
2084 		if (copyhdr) {
2085 			if (!m_dup_pkthdr(n, m, M_NOWAIT))
2086 				goto nospace;
2087 			if (len == M_COPYALL)
2088 				n->m_pkthdr.len -= off0;
2089 			else
2090 				n->m_pkthdr.len = len;
2091 			pkthdrlen = &n->m_pkthdr.len;
2092 			copyhdr = false;
2093 		}
2094 		n->m_len = mlen;
2095 		len_cp += n->m_len;
2096 		if (m->m_flags & (M_EXT|M_EXTPG)) {
2097 			n->m_data = m->m_data + off;
2098 			mb_dupcl(n, m);
2099 		} else
2100 			bcopy(mtod(m, caddr_t)+off, mtod(n, caddr_t),
2101 			    (u_int)n->m_len);
2102 
2103 		if (sb && (sb->sb_sndptr == m) &&
2104 		    ((n->m_len + off) >= m->m_len) && m->m_next) {
2105 			sb->sb_sndptroff += m->m_len;
2106 			sb->sb_sndptr = m->m_next;
2107 		}
2108 		off = 0;
2109 		if (len != M_COPYALL) {
2110 			len -= n->m_len;
2111 		}
2112 		m = m->m_next;
2113 		np = &n->m_next;
2114 	}
2115 	return (top);
2116 nospace:
2117 	m_freem(top);
2118 	return (NULL);
2119 }
2120 
2121 void
2122 tcp_sndbuf_autoscale(struct tcpcb *tp, struct socket *so, uint32_t sendwin)
2123 {
2124 
2125 	/*
2126 	 * Automatic sizing of send socket buffer.  Often the send buffer
2127 	 * size is not optimally adjusted to the actual network conditions
2128 	 * at hand (delay bandwidth product).  Setting the buffer size too
2129 	 * small limits throughput on links with high bandwidth and high
2130 	 * delay (eg. trans-continental/oceanic links).  Setting the
2131 	 * buffer size too big consumes too much real kernel memory,
2132 	 * especially with many connections on busy servers.
2133 	 *
2134 	 * The criteria to step up the send buffer one notch are:
2135 	 *  1. receive window of remote host is larger than send buffer
2136 	 *     (with a fudge factor of 5/4th);
2137 	 *  2. send buffer is filled to 7/8th with data (so we actually
2138 	 *     have data to make use of it);
2139 	 *  3. send buffer fill has not hit maximal automatic size;
2140 	 *  4. our send window (slow start and cogestion controlled) is
2141 	 *     larger than sent but unacknowledged data in send buffer.
2142 	 *
2143 	 * The remote host receive window scaling factor may limit the
2144 	 * growing of the send buffer before it reaches its allowed
2145 	 * maximum.
2146 	 *
2147 	 * It scales directly with slow start or congestion window
2148 	 * and does at most one step per received ACK.  This fast
2149 	 * scaling has the drawback of growing the send buffer beyond
2150 	 * what is strictly necessary to make full use of a given
2151 	 * delay*bandwidth product.  However testing has shown this not
2152 	 * to be much of an problem.  At worst we are trading wasting
2153 	 * of available bandwidth (the non-use of it) for wasting some
2154 	 * socket buffer memory.
2155 	 *
2156 	 * TODO: Shrink send buffer during idle periods together
2157 	 * with congestion window.  Requires another timer.  Has to
2158 	 * wait for upcoming tcp timer rewrite.
2159 	 *
2160 	 * XXXGL: should there be used sbused() or sbavail()?
2161 	 */
2162 	if (V_tcp_do_autosndbuf && so->so_snd.sb_flags & SB_AUTOSIZE) {
2163 		int lowat;
2164 
2165 		lowat = V_tcp_sendbuf_auto_lowat ? so->so_snd.sb_lowat : 0;
2166 		if ((tp->snd_wnd / 4 * 5) >= so->so_snd.sb_hiwat - lowat &&
2167 		    sbused(&so->so_snd) >=
2168 		    (so->so_snd.sb_hiwat / 8 * 7) - lowat &&
2169 		    sbused(&so->so_snd) < V_tcp_autosndbuf_max &&
2170 		    sendwin >= (sbused(&so->so_snd) -
2171 		    (tp->snd_nxt - tp->snd_una))) {
2172 			if (!sbreserve_locked(so, SO_SND,
2173 			    min(so->so_snd.sb_hiwat + V_tcp_autosndbuf_inc,
2174 			     V_tcp_autosndbuf_max), curthread))
2175 				so->so_snd.sb_flags &= ~SB_AUTOSIZE;
2176 		}
2177 	}
2178 }
2179